Finned-tube heat exchanger



Feb. 13, 1968 w. A. HALE 3,368,547

FINNEDTUBE HEAT EXCHANGER Filed om. 25, 1965 5 sheets-Sheet 1" MVML ` llINVENTOR. n//gggzmz HQ@ uy /QMToR-NEYS Feb.13,196s W,A,HALE I3,368,541v

-FINNED-TUBE HEAT EXCHANGER Filed oct. 25, 1965 5 sheets-sheet 2 t lINVENTOR. //zawZ/ fa/Ze f v y l) ATTORNEYS Feb. 13, 1968 w. A. HALE3,368,547

' FINNED-TUBE HEAT EXCHANGER Filed oct. 25, 1965 5 sheets-sheet zINVENTOR Feb. 13, 1968 w. A. HALE 3,368,547

FINNED-TUBE HEAT EXCHANGER Filed oct. 25, 1965 v 5 sheets-sheet 4INVENTOR. v

Feb. 13, 1968 W. A.; HALE 3,368,547

FINNED-TUBE HEAT EXCHANGER Filed oct. 25, 1965 5 sheets-sheet s)INVENTOR.

/f/zawZ/ /Y/*Ze UY /MATTORNEYS United States Patent() 3,368,547FINNED-TUBE HEAT EXCHANGER William A. Hale, 4503 N. Knoxville Ave.,

Peoria, Ill. 61614 Y Filed Oct. 23, 1965, Ser. No. 503,323 8 Claims.(Cl. 126-350) ABSTRACT F THE DISCLSURE A water tube type heat exchangeris provided with sheet metal fins mechanically fixed in place thereon inappropriate position to improve transfer efficiency. The fins may beemployed as spacing means, in addition to their heat transfer function,for positioning the adjacent coils of a multiple coil tube and, further,the fins may be provided with a configuration substantially controllingthe flow of heat transfer medium, such as combustion gas, along andaround the water tube coil. A number of specific embodiments of finconstruction are disclosed.

The present invention relates to heat transfer devices and is, moreparticularly, concerned with the provision of a novel ,and substantiallyimproved hot water boiler. As those skilled in the art of boilerconstruction are aware, increased efficiency in high speed watercirculation sys'- tems, as well as improved materials have led to verysubstantial simplifications in modern heating systems. Increasingattention has, accordingly, been given to the continued improvement ofsuch systems along the lines of efficiency. However, as new, morecompact, and efficient hot water boilers have developed, improvements inthe form of cost reduction have lagged behind.

By employing several novel techniques of manufacture and assembly, Ihave provided an extremely inexpensive and yet unusually highlyefficient hot water boiler. As a result of the novel configuration ofthe boiler components of my invention, increased boiler capacity isachieved in an extremely simple manner. This simplicity has verysubstantially reduced the cost a manufacture of the boiler and has, atthe same time, provided an improved over-all boiler efficiencythroughout the range of normal sizes for home heating purposes.

In accordance with the principles of my invention, a copper coil ispreformed into its final configuration in a bare, unfinned state.Utilizing this initial forming step permits the simple manipulation ofthe copper tubing. Following the forming step, a plurality of individualfins are mechanically clipped to the tubing along the length thereof.The mechanical attachment of the fins to the tubing is designed toprovide close contact between the fin l and the tube such that dippingof the tube with assembled fins clipped thereon will provide a verysatisfactory metallic bond. This is particularly true when the tubing iscopper and bonding agents such as tin or zinc are employed to provide apermanently tinned or galvanized, bonded connection between each of thefins and the tubing. By this arrangement, manipulation of the fins ontothe tubing is readily accomplished while the final positioning of thefins is rendered permanent as a result of the bonding operation.Following the bonding operation, portions of the method of manufactureof the assembled unit is novel and has minimized cost of the boilerassembly.

It is, accordingly, an object of the present invention to provide asimplified hot water boiler of improved eiciency.

Another object of the present invention is to provide an improved finnedcoil for hot water boilers or the like.

Still a further object of the present invention is to provide animproved fin element adaptable for use in heat transfer equipment.

Still a further object of the present invention is to provide a noveland improved method of assembly and disassembly of a hot water boiler orthe like.

A feature of the invention is the provision of a snap-on mechanicallyretained heat conducting fin.

Still .another feature of the invention is the provision of a preformedcoil with permanently bonded sheet metal heat conducting fins projectingtherefrom.

Still other and further objects and features of the present inventionwill at once be understood from a consideration of the attachedspecification and drawings in which various embodiments of my inventionare shown by way of illustration only, and wherein:

FIGURE 1 is a side-elevational view, in partial crosssection, of ahot-water boiler incorporating the principles of the present invention;

FIGURE 2 is a plan view, in partial cross-section, of the boilerillustrated in FIGURE l;

FIGURE 3 is an end-elevational view of the boiler constructed inaccordance with the principles of the present invention, in the samemanner as FIGURE l, but incorporating a pair of heat transfer coils andrelated burner equipment.

FIGURE 4 is a side-elevational view in partial crosssection, of a roundboiler modification constructed in accordance with the principles of thepresent invention;

FIGURE 5 is a plan view of a first form of fin ernployed in accordancewith the principles of the present invention;

FIGURE 6 is an end-elevational View of the clip shown in FIGURE 5;

FIGURE 7 is a plan view of a fin constructed similarly to the fin shownin FIGURE 5 but with a positioning tang lstruck up therefrom;

FIGURE 8 is an end-elevational view of the fin shown in FIGURE 7 inposition in a boiler;

FIGURE 9 is a further embodiment of a fin constructed in accordance withthe principles of the present invention shown in plan view;

FIGURE 10 is an end-elevational view of the fin shown in FIGURE 9;

FIGURE 11 is a plan view of a still `further modified form of the fin ofthe present invention;

FIGURE 12 is an end-elevational view of the fin illustrated in FIGURE11;

FIGURE 13 is an end-elevational view of a still further v `modified formof fin;

FIGURE 14 is a plan view of astill further form of FIGURE 15 is apartial side-elevational view of the fin shown in FIGURE 14;

FIGURE 16 is an end-elevational view of the fin shown in FIGURE 14 shownin position relative to a boiler coil; I

FIGURE 17 is a plan view of a still further embodiment of the invention;

FIGURE 18 is a cross-sectional view, in part, taken along the lineXVIII-XVIII in FIGURE 17;

FIGURE 19 is an end-elevational view of the fin shown in FIGURE 17 inits assembled relation;

FIGURE 20 is a further embodiment of a fin constructed in accordancewith the principles of the present invention;

FIGURE 21 is an end-elevational view of the fin shown in FIGURE 20 inassembled relation with boiler components;

FIGURE 22 is a plan view of a still further modified form of fin designfor use with a circular or round boiler;

FIGURE 23 is an end-elevational View of the fin illustrated in FIGURE22;

FIGURE 24 is a still further modified form of fin; and

FIGURE 25 is an end-elevational view of the fin illustrated in FIGURE24.

As shown on the drawings:

As has been above noted, boilers of the water tube type commonlyemployed in domestic heating systems have received close scrutiny fromthe point of view of cost and etiiciency in recent years. Increasinglyimproved insulation, water circulating equipment, and automatic burnerand circulation control have materially reduced the over-all size ofindividual boiler units. My own studies in the area of improving theefficiency and lowering the cost of gas-to-Water heat transfer systemshas proved that although the recent developments in these areas havebeen significant, extremely important improvements in both of theseareas are possible through the method and apparatus of the presentinvention. In accordance with the principles of the present inventionthe gas flow outside of, and around, the water tube of the boiler hasbeen directed into a more efficient heat transfer contact, and thetechnique of positioning and applying heat transfer fins directly to thewater tubes has been improved. The improved over-all system is clearlyshown in FIG- URES 1 through 4, in several embodiments, and specificfor-ms of heat transfer fins configuration are more fully illustrated inthe remaining figures.

As may be seen from a consideration of FIGURES 1 and 2, a first form ofimproved heat exchanger is comprised of a housing containing an oil orgas burner element 11 positioned at the base of a firebox or combustionchamber 12 above which a generally spiral shaped coil 15 is positioned.The coil 15 comprises a conduit 16 having an inlet connection 17, anoutlet connection 18, and a plurality of heat-conducting fins 19.Combustion gases leaving the chamber 12 circulate generallylongitudinally of the conduit 16 and, at the same time, generallyupwardly toward the fiue 20. As shown in FIG- URES 1 and 2, the coil 15is wound in a flattened spiral when viewed from above. This spiral is ofa dimension permitting the fins 19 to project immediately adjacent oneanother in the central area, a fact which can readily be seen fromFIGURE 2 where the edges 19a of the fins 19 approach each other alongthe central isle. Similarly, the exterior edges 19b of the individualfins extend substantially .against the insulation 13. In the embodimentillustrated the insulation 13 comprises a conventional fibrousinsulation such as for example the material marketed under the trademarkKaowool comprising 2200 insulation material or similar product such asCarborundum Fiber Frax insulation material. This `insulation material ispositioned inside of an additional insulating layer 14 of conventionaltype, such as for example 2 thick 1200 U.S. Gypsum oven insulationpositioned between the outermost housing wall 10a and the inside housingwall 10b.

As a result of the close `proximity of the outermost edges 19b with theinside layer of insulation, and the close proximity between thecentermost edges 19a with corresponding edges 19a of other fins, thecirculation of the combustion gases is forced into a generally helicalpath with some longitudinal movement along the longitudinal axis 15a,permitted between adjacent fins. A tortuous path is thus provided whichrequires that the combustion gases pass in intimate contact with thefins in a wiping or scrubbing manner on their way to the flue 20.

It will be clear that the lconduit 16, upon which the fins 19 arepositioned, is extremely rugged. As shown, it has no internal seams orconnections in the combustion chamber area. In addition, as will now bemore fully discussed, the individual fins 19 are bonded in an efficientheat transfer relationship in a simple, inexpensive manner permittingsimple manufacture or on-site repair of the boiler without in any wayendangering the boiler from the introduction of seams, fittings, or thelike.

I have found that as a result of the tortuous path provided in thismanner, a single copper conduit 16, formed in an output heat exchangercoil as shown in FIGURES 1 and 2, employing 7A" O.D. copper tubingcoiled as illustrated in a space having a width x, shown in FIGURE 2, of5" and a length y of 13" with six coils will produce a gross output onthe order of 50,000 B.t.u.s per hour per unit, when firing the unit withgas. The unit may readily be fired with oil by lowering the burner unit,possibly necessitating a lengthening of the combustion chamber 12 in thevertical dimension, and in such installations I have found that the sametubing arrangement will provide a gross output on the order of 56,000B.t.u.s per hour. As will be recognized by those skilled in the art,such an output is extremely high for a coil configuration of such smallsize and compactness.

A major advantage of the system and technique employed in the presentinvention is that multiples of the system may readily be achieved merelyby the addition of further coils and burners. This is readily observablefrom a consideration of FIGURE 3 where the combustion chamber 12 isshown to have a pair of identical burners 11 positioned beneath a pairof identical coils 15. The ue 20 is, as in the case of a single coilembodiment of FIGURES 1 and 2, positioned centrally in the top of thehousing 100. Essentially all of the basic components are identical,except twice in number, in the embodiment shown in FIGURE 3. Onedifference in construction is, of course, that a header is desirable forconnecting the coil inputs 17 to a single circulation input header 17a,and connecting the two outputs 18 to a joint output header. Such inputand output headers may, of course, take conventional form and as shown,are preferably positioned externally of the housing 10 in the generalposition shown by the header connections 17a and 18a of FIGURE 1. It hasbeen found that the utilization of two burners with two coils in themanner illustrated provides a ygross output rating on the order of95,000 B.t.u.s per hour that similar utilization of three coils withthree burners provides a rating of 145,000 B.t.u.s per hour, foursimilar units a rating of 192,000 B.t.u.s per hour and the combinationlof five similar units will provide a gross output rating ofapproximately 240,000 B.t.u.s per hour, all when fired with gas. Asingle thermal switch 11a senses the water temperature in the coil andshuts off the burner 11 upon a tube temperature of 300 F. indicatinglack of Water therein. With this system, it becomes extremely simple toconstruct an entire range of boiler units with an absolute minimum ofdifferent parts.

In the embodiment of the boiler shown in FIGURES 1 and 2, baffles areprovided at the front and rear of the coil 15 in the form of ceramicseparators 21. Such a ceramic lining may encircle the coil 15 in theform of ceramic sides 22, as well. A second embodiment of peripheralcoil construction is found in the cylindrical boiler embodiment ofFIGURE 4. As may readily be observed from FIGURE 4, the peripheral edgesof the individual fins substantially contact the Kaowool insulationdirectly. In this form of the invention, which will be more fullydescribed below, the individual fins completely encircle the coilproviding a substantially continuous flow path without baflies. Whensuch substantial contact between the individual fins and the Kaowoolinsulation is employed in the embodiments of the invention illustratedin FIGURES 1, 2 and 3, ceramic elements 21 and 22 are eliminated andiins 19 are snapped into position continuously around the ends of thecoil. Under these circumstances, such individual tins 19 positioned 'atthe `ends of the coil may take the form of a one-piece continuous iincovering substantially the end of the coil as a generally segmentalcircular 1in larger than that of the same circular conduit-grippingshape as illustrated in connection with the burner of FIGURE 4.

Contrary to conventional boiler construction, the fins of the presentinvention run generally longitudinally of the tube and transversely tothe direction of intended gas flow relative to the axis a of the coil15. In conventional practice, -ins are generally applied in some mannerto the water tube such that the `fins lie transverse to the longitudinalaxis of the water tube and in a plane running substantially parallel tothe axis of the coil. I have found that the provision of the fingenerally longitudinally of the conduit and transversely positionedrelative to the coil axis provides a much more tortuous path and greatlysuperior wiping action of the flue gases relative to the water coil.This in turn has provided a substantially improved over-all boilerefiiciency without an increase in space requirements. Still further, .aswill now become apparent, the utilization of the longitudinallyextending iin has permitted a greatly improved iin-to-conduit connectioncapable of simple manufacture and inexpensive assembly.

Preferably, the individual fins 19 are formed of stamped sheet metalsnapped over a tubular form conduit into a stable, spring-retainedcondition on the conduit. Preferably, the retaining force formaintaining the individual 1in rmly on the conduit is supplied by thefin itself. A primary form of finis illustrated in FIGURES 5 and 6. Asmay there be seen, the iin 19 comprises a pair of laterally extendingears 19e joined by a segmental cylindrical portion 19d struck on a curveabout a center 19e. As shown, the segmental cylindrical portion 19dextends over-center on opposite sides of a diametral line 19j so thatthe dimension Z forming a restricted neck portion is of smaller lengththan the diameter of curvature of the portion 19d. Accordingly, the fin19 may be snapped over the conduit into a friction lit position.

In assembling a heat transfer coil, the coil is initially formed in agenerally helical form with a continuous length of conduit. After takingthe iinal generally helical form, the individual ns are snapped intoplace and pivoted into the position generally illustrated in FIGURES 1and 2. After this assembly procedure the coil, comprising the conduitwith the assembled fins, is preferably dipped into a tin or zinc bath orlike metallurgical treatment to provide a bond between the individualfins and the conduit. This bond provides an extremely efficient heattransfer medium between the tins and the conduit. Following themetallurgical treatment, the assembled coil is inserted from theright-hand wall of the boiler as Viewed in FIGURE 1, by removal of thefront wall 10c of the housing 10. In such assembly, the inlet conduitportion 17 may have a dowel, not shown, inserted therein and projectingsubstantially therebeyond for insertion into the hole 10d in the sidewall of the boiler. This acts as a guide and permits extremely rapidinsertion of the coil into the position shown in FIGURE 2. During suchassembly the header 18a is not assembled with the outlet portion 18 ofthe conduit and following insertion of the coil into positions, the sidewall portion 10c is slipped over the extension 18 into the positionsh'own and rigidly retained in such position by assembly screws, notshown, and slip-on foot connections 10e and 10f. As a result of such aslipon connection, the wall 10c may readily be removed by removal of theheader 18a, for cleaning of the coil in position in the boiler.Alternatively, of course, the entire coil may readily be removed fromthe boiler for repair or cleaning by removal of the header 17a andmovement of the coil and the wall 10c as a unit toward the right.

-6 If found desirable, a positioning guide pin 25 may be rigidlyimbedded in the lwall 10b for co-operation with ceramic locator 21 or,alternatively, with a bracket (not shown) welded or otherwise secured toconduit 16.

Due to the fact that the coil 15 of the boiler of the present inventioncomprises a plurality of turns, the fins may be employed as a device foraccurately spacing the coils. Such an arrangement is shown in theembodiment of FIGURE 7 where lin 119 is shown as having an upstruck tang119a. The tang 119a co-operates with the next adjacent turn of the coilconduit 16 to space adjacent coils as shown in FIGURE 8. Inconstructions in which the turns of the coil 15 are accurately and xedlyspaced by external means, the fin need not comprise an arrangementhaving an over-center retaining action. Such an arrangement is shown,for example, in FIGURES 14, l5 and 16. There, the iin 219 is providedwith an upstruck adjustably bendable tang 219a having an arcuate portion219b which co-operates with the next adjacent turn of the coil conduit16 in the manner illustrated in FIGURE 16. In view of the curved shapeof the tang 219b, the turns of the coil will accurately locate andposition the fins 219. During the metallurgical bonding operation, theins become integrated with the tubing and subsequent variation andseparation between the turns of the coil 15 will not cause separation ofthe ns 219 from the conduit 16.

A further modification of the fin 19 is illustrated in FIGURES 9 and 10where 1in 319 is illustrated. There, a very substantial pierced opening320 is provided. The opening operates to substantially relieve theamount of Vmaterial in the arcuate portion 319d thereby rendering theassembly of the device to the conduit simpler by increasing theflexibility of the fin. Under such circumstances the thickness of thetin material may be increased, if desired, without increasing thediliiculty of manual assembly. Another technique of rendering thelateral portions of the iin more rigid is illustrated in FIG- URES 11and l2 where the laterally extending portions 419C of the iin 419 arebent backwardly upon themselves to provide a double thickness. Thisarrangement may be employed with a relatively thin arcuate portion 419dto, again, provide a relatively flexible arcuate portion with asubstantial, relatively stili, laterally extending iin portion.

In some installations it is desirable to increase the restriction of gasflow beyond that available with the arrangements above described. Onetechnique of accomplishing this is to provide for a downward deflectionof the lateral iin portions in the manner illustrated in FIG- URE 13. Asthere shown, portions 519e deflect downwardly from the arcuate portions519d. This downward deflection is in the upstream direction of gas flowand requires gas to pass backwardly upon itself and outwardly before itcan proceed upstream, as illustrated by the arrow 520. It will be clearthat this downward positioning or deection of the fins may be employedwith any of the fin forms of the present invention.

A further embodiment of fin construction provides a particularly simpleassembly procedure. For example, the arrangement shown in FIGURES 17through 21 incorporate a separate spring element for maintaining thefins in position on the tube. This separate spring element permitsutilization of a 1in not having a snap-over feature and at the same timepermits a very stable, assembled, relationship. In the embodiment shownin FIGURES 17 through 19, a wire spring 621 is employed with fin 619.The wire `spring 621 has an end projection 622 that cooperates with anupstruck tunnel 619:1 and locating guide tab 619b. The wire spring 621is provided with an arcuate form extension 623 co-operating with thenext adjacent conduit 16 and co-operates therewith to maintain the iin l619 pressed downwardly in its position against conduit 16.

Similarly, in the embodiment shown in FIGURES 20 and 21, the fin 719 isprovided with an upstruck portion 719a that acts in co-operation as aspacer with the next adjacent conduit 16. The lin 719 is maintainedresiliently in contact with the lower coil conduit portion 16 by meansof a resilient spring 721 that is provided with hook portions 722 thatproject through apertures 719d for cooperation wit-h fin 719. Inassembly, the spring 721 is passed beneath the lowermost conduit portion16, upwardly through the aperture 719b on one side of the fin to a pointat which it projects substantially therebeyond. With the fin and springthus positioned, the other end of the spring is pressed upwardly intoaxial alignment with the other aperture 719b and is slid relative to theconduit portion 16 through the other aperture 719b into the assembledposition shown in FIGURE 21.

The relatively flexible form of spring employed in the embodiment ofFIGURES l7 through 21 may be achieved by the use of a relativelyflexible upstruck tangv portion of the fin itself as shown in theembodiment of FIGURES 24 and 25. As there shown, the fin 819 is providedwith an upstruck tang spring portion 819a which projects in cantileverfashion slightly beyond the center condition. As a result the fin may besnapped over the conduit 16 by movement .in the direction of the arrow820. The fin construction permits simple assembly and an absoluteminimum of parts. It will, of course, be apparent that if desired astill further tang may be upstruck for co-operation as a spacer with thenext adjacent turn of the coil.

In the fin configurations above discussed, the fins have been providedwith a generally straight segmental cylindrical portion for co-operationwith a generally straight portion of the coil conduit. In constructions.in which the boiler is generally circular as shown in the embodiment ofFIGURE 4, or in which the fin is constructed for attachment to the ends,or arcuate portions of coils such as illustrated in FIGURES l and 2, itis desired that the n be curved to co-operate with the curved portion ofthe coil conduit.

An example of such a fin is found in FIGURES 22 and 23. As there shown,the fin 919 is provided with an arcuately configurated segmentalcylindrical portion 919d. It will be apparent that fins of the curvedtype as shown in FIGURES 22 and 23 may readily take any of the forms inthe remaining figures.

In the specific embodiment of the boiler incorporating a circular form,and .illustrated in FIGURE 4, it is necessary to employ the form of findescribed in FIGURES 22 and 23. In view of the fact that a relativelylarge diameter coil turn is employed, it is desirable that the centralarea of the coil be filled with a gas flow controller. This controllertakes the form of a generally cylindrical plug 30. Preferably the plug30 has a helical flange 31 in the form of a thread projecting around itsperipheral surface. The thread 31 cooperates with the inwardly facingedges 919a to provide a restriction to gas flow. The plug is preferablyconstructed of ceramic and is provided with ears 32 which act as stopsagainst the uppermost turn of the coil 116 to position the plugaccurately with respect to the individual coil turns. The burner 111may, of course, be of any conventional form and forms no part of thepresent invention.

The improved boiler and fin configuration, as well as technique ofboiler construction and assembly, described above are of greatimportance in providing an inexpensive highly eflicient hot water boilersystem. It will be apparent to those skilled in the art that the finsmay be constructed of a wide variety of materials, for example,stainless or spring steel, which provide very strong snap-actionretention. Alternatively, the fins may be constructed of such materialsas copper, if desired. Copper is particularly satisfactory whereseparate springs are employed, such as for example in the embodimentsshown in FIGURES 17 through 2l. Similarly, although the fins have beendescribed as metallurgically bonded to the coil turns by means of amolten dip of tin or zinc, other fastening means may be employed. Forexample, the fins may be spotwelded, brazed, soldered, or otherwisesecured to the conduit if desired. Since many variations will be readilyapparent to those skilled in the art from the numerous embodiments abovedescribed, it is my intent that the scope of the present invention belimited solely by that of the hereinafter appended claims.

I claim as my invention:

1. In combination in a heat exchanger, means providing a source of hightemperature combustion gas, a gas outlet and means Iproviding a gas flowcurrent from said source to said outlet, a fluid conducting tube formedin a coil about an axis generally parallel to the axis of combustion gasflow, a plurality of fins in heat transfer contact with said tubing andextending laterally outwardly therefrom transverse to the direction ofgas flow and generally parallel to the axis of the tubing at theircontact junction therewith, said fins extending outwardly and inwardlyof the coil in both directions substantially restricting the open flowarea outside of the coil and inside of the coll whereby the gas flowwill follow generally the contour of the fluid conducting tube.

2. The structure set forth in claim 1 wherein said fins are mechanicallymaintained in contact with said fluid conducting tube and aremetallurgically lbonded thereto.

3. A heat transfer element comprising a conduit formed in a coil havinga plurality of turns along its longitudinal axis for distribution of aheat transfer uid, fins secured to said conduit and projecting laterallythereof and generally parallel to the axis of the conduit, andmechanical means for retaining said fins on said conduit, the innermostand outermost edges of the fins being substantially constant along saidcoil and the innermost edges of the fins substantially blocking theinterior of said coil.

4. In combination in a heat exchanger, means providing a source of highcombustion gas, a gas outlet, and means providing a gas flow currentfrom said source to said outlet a fluid conducting tube formed in a coilabout an axis generally parallel to the axis of combustion gas flow, aplurality of fins in heat transfer contact with said tubing andextending laterally outwardly therefrom transverse to the direction ofgas flow and generally parallel to the axis of the tubing at theircontact junction therewith, and means on said fins co-operable withspaced turns of said coil to retain said fins between adjacent coils inmechanical contact with and positioned by said adjacent coils.

5. In combination in a heat exchanger, means providing a source of highcombustion gas, a gas outlet, and means providing a gas flow currentfrom said source to said outlet a fluid conducting tube formed in a coilabout an axis generally parallel to the axis of combustion gas flow, aplurality of fins in heat transfer contact with said tubing andextending laterally outwardly therefrom transverse to the direction ofgas flow and generally parallel to the axis of the tubing at theircontact junction therewith, means on said fins co-operable with spacedturns of said coil to retain said fins between adjacent coils inmechanical contact with and positioned by said adjacent coils, andmetallurgical bonding means for bonding said fin to at least one of thecoils with which it has contact.

6. A heat transfer iin for cooperation with a tubular heat transferconduit, which comprises a sheet of heatconducting material having achannel stamped therein to co-operate in surface-to-surface contact withsaid conduit, and means integral with said sheet and co-operating withsaid conduit whereby said fin snaps mechanically into position on saidconduit in a mechanically secure position thereon, said last-named meanscomprising a tang struck from the body of said sheet and snapping over aprojecting portion of said conduit for applying pressure to oppositesides of said conduit to retain said fin thereon.

7. In combination in a heat exchanger, a fluid conducting conduit formedin a coil about an axis generally parallel `to the axis of combustion ofgas flow in said heat exchanger, a plurality of fins in heat transfercontact with said conduit and extending laterally outwardly and inwardlytherefrom transverse to the direction of gas flow and generally parallelto the axis of the conduit at their contact junction therewith, aninsulated housing surrounding said coil and in immediate proximity tothe outer edges of said tins whereby gas ow generallyv parallel to thesaid axis and outside said tins, said ns projecting inwardly of saidcoil to substantially block free flow of said gas longitudinally of saidcoil within the contines thereof whereby combustion gases are restrictedto tortuous paths through said coil. Y

8. In combination in a heat exchanger, a fluid conducting conduit formedin a coil about an axis generally parallel to the axis of combustion ofgas flow in said heat exchanger, a plurality of fins in heat transfercontact With said conduit and extending laterally outwardly and inwardlytherefrom transverse to the direction of gas flow and ygenerallyparallel to the axis of the conduit at their Contact junction therewith,said fins extending substantially Icontinuously along said coil conduitto provide said conduit with at least one completev spiral turn,

' an insulated housing surrounding said coil j and in immediateproximity to the outer edges of said ns whereby combustion gas owgenerally parallel to the said axis and outside said tins is restricted,said ns projecting in- 10 wardly of said coil to substantially blockfree flow of said gas longitudinally of said coil within the confinesthereof whereby combustion gases are restricted to tortuous pathsthrough said coil.

References Cited UNITED STATES PATENTS 473,176 4/1892 Holden 165-183672,412 4/ 1901 Birdsall 165-181 1,942,211 1/1934 Hartwig 122-3672,036,961 4/ 1936 Collier 165-181 X 2,086,647 7/ 1937 Sterrick 122-250 X2,203,718 6/1940 Burch 165-168 X 2,205,984 6/1940 Kromas 165-1483,219,017 11/1965 Thybault 122-250 FOREIGN PATENTS 604,025 8/ 1960Canada. 403,899 7/ 1934 Great Britain.

ROBERT A. O'LEARY, Primary Examiner. A. W. DAVIS, Assistant Examiner.

